This invention relates to a method of making acoustic devices of the nature of loudspeakers and loudspeaker drive units and comprising resonant panel-form members capable of producing an acoustic output when excited with bending waves, and to acoustic devices made by the method.
The basic patent teaching for such panel-form acoustic members, known as xe2x80x9cdistributed modexe2x80x9d or xe2x80x98DMxe2x80x99 devices, is in International patent application WO97/09842 of New Transducers Limited.
It is known to suspend such panel-form members on, for example, a frame or chassis by means of a resilient suspension fixed adhesively to the edge of the member. It is an object of the present invention to facilitate the mounting and suspension of resonant panel-form acoustic members relative to framing which may, for example, be a shallow enclosure or a so-called basket or chassis.
DM panel-form loudspeakers emit acoustic radiation from both sides of the panel, i.e. are bi-polar, and to facilitate positioning of the loudspeaker in a room, e.g. against a back wall, the rear radiation can be blocked or attenuated by placing the panel in a sealed box with a flexible surround or suspension round the panel perimeter to mount the panel in the box. This prevents any destructive interference from reflecting surfaces behind the panel. The panel surround or suspension may be a strip of flexible foam with adhesive tape on both sides.
However, in such an arrangement, standing waves may be set up in the rear enclosure which can adversely affect the frequency response of the panel. These standing waves can be damped by filling the enclosure with an acoustic absorber, e.g. of soft foam material, for example flexible polyester or polyether.
It is another object of the invention to provide a method of making an acoustic device comprising a resonant panel-form member in which a suspension for the panel and an acoustic absorber are combined.
From one aspect the invention provides a method of making an acoustic device in the form of a loudspeaker drive unit having a resonant panel-form member adapted to provide an acoustic output when excited with bending wave energy, comprising forming a resilient suspension for the panel-form member by moulding and simultaneously fixing the resilient suspension to the panel-form member.
The moulding may be with the aid of compression and/or heat and using a foamed plastics or rubber as the starting material for the suspension, or may comprise injection moulding of an elastomeric material.
Fixing of the suspension to the panel-form member may be accomplished with the aid of an adhesive or may involve direct injection of the suspension onto the panel-form member. The resilient suspension may be fixed to a peripheral margin of the panel-form member.
The method may comprise moulding a marginal portion of a block of soft or resilient foamed plastics or rubber by pressure and/or heat to form the suspension and such that a portion of the block of foamed plastics or rubber forms an acoustic absorber for attenuating or absorbing the acoustic output from one side of the panel-form member.
Where the suspension is injection moulded, a rigid support member may be co-moulded or integrally moulded or otherwise attached to the resilient suspension at a position spaced away from the edge of the panel-form member to provide a support for fixing the suspension in position, e.g. in an enclosure or in or on a frame or chassis. The rigid support may be in the form of a member extending round the periphery of the panel-form member as a continuous member or may be discontinuous where a suspension in the form of discrete suspension components or elements is required. A continuous suspension may provide an air or dust seal.
The fixing of the support to the enclosure or frame or chassis may be by clamping, adhesive, fasteners or the like or by a combination of these fixing methods.
Where the suspension is injection moulded it may abut the edge of the panel-form member or may surround or partially surround the edge of the panel-form member. The resilient suspension may also be such as to surround or at least partially surround the rigid support member. Locating elements in the form of protrusions or recesses or apertures may be moulded into the injection-moulded suspension or may be provided in the rigid support to locate the suspension in the frame, chassis or enclosure.
The suspension may be formed such that the suspension is an interference fit in or on the frame, chassis or the like and so that tension and/or compression is applied to the suspension when it is mounted to its frame, chassis or the like to enhance the contact therebetween.
From another aspect the invention is a loudspeaker drive unit made by the method described above.
From yet another aspect the invention is a loudspeaker comprising a drive unit as defined above. Preferably the panel-form member is constructed generally in accordance with the teachings in International patent application WO97/09842 and counterpart U.S. application Ser. No. 08/707,012, filed Sep. 3, 1996, and is thus a distributed mode device.